1. Field of the Invention
This invention relates to thrust bearing washers for rotary cone rock bits.
More specifically, this invention relates to a means to prevent rotation and to mechanically lock in place an intermediate thrust bearing washer radially disposed between a roller cone and a journal, the washer being primarily designed to take axial thrust loads.
2. Description of the Prior Art
There are a number of prior art patents that provide some means between rotating cones and their respective journals to take axially directed outthrust loads directed against radial surfaces formed on the journal bearings.
It is within the state of the art to provide a hard metal bearing surface on radially disposed areas of the journal and the cone by either depositing hard metal material to either the end of the journal or within radially disposed surfaces in the cone. The deposited hard metal material is subsequently machined to provide a smooth bearing surface between the journal and the rotating cone.
The problems that emerge utilizing the foregoing techniques are many. For example, when hard metal material is metallurgically deposited either within the cone or on radially disposed surfaces of the journal, the heat generated causes stress risers that can result in cracks, especially in the rotating cones. In addition it is difficult, costly and time-consuming to machine these rough, hard metal deposition surfaces to form good bearing surfaces essential to the proper operation and longevity of the rock bit.
The present invention overcomes this difficulty by simply providing a hard metal, nonrotating locked-in-place disc between the journal and the cone.
U.S. Pat. No. 3,720,274 teaches the use of an intermediate thrust bearing washer freely disposed within radially aligned surfaces formed between the end of a journal bearing and a rotating cone associated therewith. The thrust bearing serves to support thrust loads and stabilizes the cone cutters. The intermediate thrust bearing washer is allowed to float between the pin and the journal. A difficulty with this arrangement is that, as the rock bit wears in an operating mode, the thrust washer begins to gall, causing the bearing to eventually fail.
The previously filed patent application obviates the problem of the floating thrust washer in that a hard metal radial surface is provided in the form of an elliptical washer that is nested within a complementary elliptical cavity formed in the cone so that it will not rotate. The elliptical washer thereby provides a stable thrust bearing surface. Moreover, no additional rotating parts are necessary and problems associated with hard metal deposition methods, i.e., cracking and uneven heat distributions through the cone, are essentially eliminated.
While the elliptical disc or washer and matching recess is a decided improvement over the prior art, the present invention is yet another improvement over the related application as well as known prior art.
The edge of the elliptical disc of the present invention is chamfered. The larger elliptical peripheral edge of the disc is first placed in a complementary elliptical recess formed in the cone. The smaller peripheral edge of the disc defines the bearing surface adjacent the radially disposed bearing surface of the journal. The elliptical recess in the cone is also chamfered to mate with the chamfered surface formed on the peripheral edge of the disc. The disc is first aligned with the elliptical recess or cavity within the cone, dropped into place within the cavity, followed by rotation of the disc within the recess. The major axis of the elliptical disc is now rotated so that it no longer is in parallel alignment with the major axis of the elliptical cavity within the cone. The chamfered edge of the disc now registers with the chamfered surface formed within the cone, thus locking the disc within the cone. The disc or washer will not rotate nor can it become dislodged from its elliptical cavity; a possibility with the previously filed application if enough wear occurs between the rotating cone and its respective journal during operation of a rock bit.